In recent years, wireless power supplies have become widespread as a method to supply electric power to electronic apparatuses. As a wireless power supply, there exist two types, i.e., an MI (Magnetic Induction) type and an MR (Magnetic Resonance) type. The MI type includes two standards, i.e., the standard “Qi” established by the WPC (Wireless Power Consortium) and a standard established by the PMA (Power Matters Alliance) (hereinafter referred to as the PMA standard), which are currently mainstream standards.
FIG. 1 is a diagram showing the configuration of a wireless power supply system 100R in compliance with the PMA standard. The power supply system 100R includes a power transmitter (TX) 200R and a power receiver (RX) 300R. The power receiver 300R is equipped in an electronic apparatus such as a mobile phone, a smartphone, an audio player, a game machine, a tablet terminal or the like.
The power transmitter 200R includes a transmission coil (primary coil) 202, a driver 204, a controller 206, and a demodulator 208. The driver 204 includes an H bridge circuit (full bridge circuit) or a half bridge circuit and applies a drive signal S1, specifically a pulse signal, to the transmission coil 202. An electromagnetic power signal S2 is generated in the transmission coil 202 by a drive current flowing through the transmission coil 202. The controller 206 generally controls the overall operation of the power transmitter 200R. Specifically, the controller 206 changes transmission power by controlling a switching frequency of the driver 204 or a duty cycle of switching.
The power receiver 300R includes a reception coil 302, a rectification circuit 304, a smoothing capacitor 306, a modulator 308, a load 310, a controller 312, and a power supply circuit 314. The reception coil 302 receives the power signal S2 of the transmission coil 202 and transmits a control signal S3 to the transmission coil 202. The rectification circuit 304/the smoothing capacitor 306 rectifies/smooths a current IRX induced in the reception coil 302 in response to the power signal S2 to convert the current IRX to a DC voltage VRECT.
The power supply circuit 314 uses the power supplied from the power transmitter 200R to charge a secondary battery (not shown) or steps up or down the DC voltage VRECT to supply it to the controller 312 and the load 310.
In the PMA standard or Qi standard, a communication protocol is established between the power transmitter 200R and the power receiver 300R. Therefore, information can be delivered by the control signal S3 from the power receiver 300R to the power transmitter 200R. The control signal S3 is transmitted from the reception coil 302 (secondary coil) to the transmission coil 202 in the form of an FSK (Frequency Shift Keying) or ASK (Amplitude Shift Keying) signal by using backscatter modulation.
The control signal S3 contains power control data (also referred to as packets) indicating the amount of power supplied to the power receiver 300R, data indicating specific information of the power receiver 300R, and the like. The demodulator 208 demodulates the control signal S3 contained in the current or voltage of the transmission coil 202. The controller 206 controls the driver 204 based on the power control data contained in the demodulated control signal S3.
The PMA standard (parent standard) includes three children standards, i.e., PMA-1, PMA-3, and PMA-4. The inventors of the present application have examined the design of the power receiver 300R supporting the PMA-1, PMA-3, and PMA-4 standards and the Qi standard.
Since frequencies used in the PMA-1, PMA-3, and PMA-4 standards and the Qi standard are different from each other, communication cannot be established between the power transmitter 200R and the power receiver 300R until the standards (protocols) are determined. Therefore, the power receiver 300R requires the ability to automatically determine a standard which the power transmitter 200R complies with, without relying on means such as communication or the like, immediately after being placed on a charging stand of the power transmitter 200R.